REPRODUCTIVE SYSTEM. 109 



ORGANS OF GENERATION. 



Testicle. A circumscribed collection of sperm cells is called 

 a testicle. Its cells are free, as in Tethya, or arranged loosely 

 to one another between folds of membrane peritoneal or 

 otherwise, as in most Radiata and marsipobranchiate fishes ; 

 or line either straight or convoluted follicles, as in most Mol- 

 lusca, Articulata, and Yertebrata. In the first two groups 

 the filaments are discharged adventitiously without duct, i.e. 

 by bursting through capsule of organ. In the majority of the 

 last they pass along a well-defined and commonly tortuous 

 canal (vas deferens), which opens by an independent point 

 (genital pore), as in cartilaginous fishes and most Inverte- 

 brata, or joins urethra near its termination, as in the majority 

 of Vertebrata. The appendages to such a canal, when present, 

 may be follicular (urethral), convoluted (vesiculse seminales), 

 racemose (prostate body and glands of Cowper). 



Ovary. A circumscribed collection of ova is called an 

 ovary. It bears a marked external resemblance to testicle 

 when cells are free, as in Tethya, or loosely held together 

 without oviduct between festoons of membrane, as in Ra- 

 diata and marsipobranchiate fishes. The resemblance is less 

 decided when the cells partially or entirely line the blind ex- 

 tremity of a tube, the contracted continuation of which forms 

 the oviduct, as in majority of osseous fishes, or where the 

 cells are supported by a distinct cellular or fibrous stroma 

 distinct from oviduct, as in other Yertebrata. In Yertebrata 

 each oviduct may unite with its fellow in median line, as in 

 Mammalia, or continue to outlet separately, as in others. 



"When an organism possesses both sexual elements it is 

 said to be hermaphroditic (bi-sexual, monoecious, androgy. 

 nous), when one cell only unisexual (dioecious). Although 



whilst the male is at all times fit for propagation. In others, constituting 

 the majority of instances, the male organs are subject to the same periodical 

 increase of activity as the female. The male in these animals is usually in 

 heat at an earlier period than the female. (Thomson.) 



